Hiren and I hosted our first happy hour event tonight, which turned out quite well.  Around 10 people showed up who worked in different domains of technology.  All very social and intelligent people.  

Selecting people very carefully and personally inviting them seems to be the way to go to create a certain kind of experience, an altered (social) reality of sorts.  Finding the right mix of people so that everyone is happy and gets to meet new/interesting people really is a fascinating art.   Now, thinking about the experience we had today, it might be fun to go and host a slightly larger event like a mini-conference.  Use speakers/DJs to attract people (and have them bring their own posse as well) and learn how to organize on a grander scale. 

I realize, much of good event planning and creating a fun social environment boils down to the details.  Are people sitting or standing, is there alcohol or not, is it a bar, or someone's home.  All of these things make for a radically different ambiance.  As Leila mentioned, perhaps it would be a good idea to consult with an event planner, who has many years of experience with these things. 

Either way, we're learning a lot and having a lot of fun hosting these events.